initfromthreadtest fail on Ubuntu 22 x64 about bdwgc

[ivmai]

Reproduced locally: ./configure --enable-gc-assertions --disable-shared && make -j check CFLAGS_EXTRA="-O0 -g -D _FORTIFY_SOURCE=2 -D FIND_LEAK -D SKIP_LEAKED_OBJECTS_PRINTING"
Output:
Signals delivery fails constantly at GC #1

[ivmai]

The scenario of the failure (on Linux):

• Find-leak mode is on
• pthread_create/join primitives are not redirected
• GC is initialized from a thread other than primordial
• that thread is terminated (but not unregistered as the 1st one in GC)
• the primordial thread exits and launches GC_exit_check
• GC_gcollect tries to suspend the terminated thread by sending a signal
• the signal is not delivered but pthread_kill just returns zero
• the signal sending is retried until aborting with the proper message.

The proposed solution (workaround) is not to call GC_gcollect at the process exit (in the find-leak mode) if GC_init was called from a thread other than primordial one.

[ivmai]

the signal is not delivered but pthread_kill just returns zero

Such behavior is first observed on Ubuntu 22.04 (Jammy) x64.

[ivmai]

The solution should also solve #533 (because no need to modify GC_in_thread_creation inside GC_exit_check).